This invention relates generally to the construction of concrete slabs. More specifically, the invention relates to improved screed rails for use as forms in the construction of concrete slabs.
In the construction of concrete slabs, it has long been the practice to use forms to define the area into which the concrete slab is to be poured. The forms serve to contain the concrete mixture when it is poured and while it hardens. When a large slab is to be poured, forms are commonly used to divide the slab into smaller subsections, each of which is poured separately.
Temporary forms, such as wooden planks, have been used for many years. However, there are a number of disadvantages that are associated with the use of temporary forms. Most notably, if concrete is poured into adjacent subsections at the same time, it is difficult, if not impossible, to remove temporary forms from between the subsections once the concrete has hardened. It is therefore necessary to avoid pouring concrete into adjacent sections at the same time. A further disadvantage of temporary forms is that once the slab is completed, the forms must removed, and then either be transported away from the job site, or otherwise disposed of.
Many of these problems have been remedied through the development of permanent containment forms, or screed rails. These screed rails, which are made primarily of concrete, can be used to define the area into which the concrete slab is to be poured, and to contain the concrete mixture during pouring and hardening operations. Unlike temporal forms, however, they are left in place after the concrete is poured, becoming part of the finished slab. As a result, a slab can be poured more easily, with adjacent subsections being filled with concrete simultaneously. Upon drying, the concrete slab simply adheres to the screed rails, which in essence become part of the slab. U.S. Pat. Nos. 4,884,384, 4,576,510, 4,598,517 and 4,950,434 are incorporated here by reference, to detail, inter alia, the construction and use of such screed rails.
In general it is necessary to provide occasional seams or gaps between the subsections of a concrete slab, in order to allow the slab to contract or expand in response to volume changes or temperature fluctuations. In the absence of such gaps, the slab may crack or buckle as it expands or contracts in response to volume or temperature changes. In situations where permanent screed rails are used, it has previously been known that a debonding agent can be sprayed along one side of a rail to prevent the concrete slab from adhering to that side of the rail. When this is done, a gap is formed between the slab and the screed rail, since the concrete slab typically pulls away from the rail as it dries.
However, one problem that has been found to exist in the construction of concrete slabs in general is that the seams or gaps between sections of a slab are prone to physical damage, referred to as spalling, when the slab is subjected to large downward forces. Such forces may, for instance, be created when a forklift or other such vehicle rolls across the slab. These problems are especially severe in situations involving the use of heavy forklifts having metal wheels with small diameters, since the heavy downward force that is exerted against the slab by the forklift is focused onto a very small area.
It is therefore an object of this invention to provide a permanent screed rail assembly for use in the construction of concrete slabs, wherein the rail assembly will protect against structural damage along the portions of the slab edges that are exposed to these forces, while providing the ability for the slab to expand or contract in response to volume or temperature changes.